(i) Field of the Invention
This invention relates to a hydraulic servo drum for friction clutches of vehicular automatic transmissions.
(ii) Description of the Prior Art
Generally, a hydraulic servo drum for friction clutches consists of an outer cylinder portion with an inner spline on the inner periphery thereof, an inner cylinder portion having a ring groove formed on the outer periphery thereof for fixing a retainer ring for the return spring of the hydraulic servo piston and provided with an oil passage for supplying line pressure to the hydraulic servo, and an annular plate portion connecting the outer and inner cylinder portions with each other and formed integrally with these cylinder portion by casting, coupling and releasing the hydraulic servo drum of a friction clutch relative to another component part by supplying or draining the line pressure.
In a case where a servo drum of such a construction is used for a friction clutch C2 which is operated at the time of shifts between the second and third speeds, however, the so-called shift shocks occur upon engagement and release of the clutch. In order to minimize the shift shocks, it is necessary to provide an appropriate piston area. In addition, the friction members (clutch plates) which are splined with the outer peripheral cylindrical portion vary in size and number depending upon the type of the vehicle. It follows that the hydraulic servo drum of the friction clutch, which is cast in the form of an integral structure, has to be remodeled almost in its entirety to cope with the change in size or number of the clutch plates, lacking versatility in practical applications.